Many useful applications, such as the detection of radioactive material, computer-assisted tomography (“CAT”), digital radiology, optical detectors, etc., rely on the detection of ionizing radiation (e.g., X-ray and gamma-ray photons and/or high energy particles—both neutral and charged) as well as “non-ionizing” photons. Non-ionizing photons, sometimes referred to as “optical” photons, are photons generally falling within the energy range from the ultraviolet (“UV”) to near-infrared (“IR”), and are commonly detected by various types of devices such as complementary metal-oxide-semiconductor (“CMOS”), charge-coupled devices (“CCDs”), avalanche photodiodes (“APD”s), photomultiplier tubes (“PMT”s), etc. Generally, the low energy end of the X-ray region begins at about 10 nm, which also approximately defines the high energy end of the “optical” photon region. However, different described energy regions broadly overlap and so descriptive terms such as “ionizing” and “non-ionizing” and “optical” in reference to a type of radiation are merely used to label a spectral region or particle energy but are not narrowly defined. For example, a given UV photon can be both ionizing and non-ionizing depending upon the interacting media. Even photons in the “visible” region can be ionizing with respect to certain materials.
Many prior art radiation detectors are proportional detectors. In general, proportional detectors store charge in capacitors or other means, and the total amount of stored charge is proportional to detected radiation. Proportional detectors operate on the principle of linear gas multiplication, and the final charge measured is proportional to the number of original ion pairs created within the gas by the incident radiation, which is proportional to the energy of the incident radiation. Proportional detectors typically require amplification circuitry in order to measure the charge.
Recently, new types of proportional gas-based radiation detector devices have been developed, including micropattern gas detectors such as cascaded Gas Electron Multipliers (“GEM”). These devices, which have been under development primarily for use in high-energy and nuclear physics, have many desirable properties as proportional gas detectors, but are limited to gains on the order of about 106. Their use however, has been held back in large part due to avalanche-induced secondary effects associated with ion, electron, photon and metastable species feedback, as well as photocathode degradation caused by ion impact.
Based on the foregoing, there is a need for a radiation sensor with high resolution capability, fast pixel response, minimal dead-time, high gain, improved radioisotope identification, low power consumption, a thin profile and physically rugged, that can be manufactured in large sizes relatively inexpensively.